1. Field of the Invention
The present invention relates to a side airbag device that restrains an occupant in a vehicle seat from a lateral side when an impact is imposed on the vehicle.
2. Description of the Related Art
In recent years, most vehicles are standard-equipped with airbags. Airbags are safety devices that operate in an emergency situation such as vehicle crashes and are inflated and deployed with gas pressure to receive and protect an occupant. Airbags come in various types depending on their installed position and their purpose. For example, a front seat driver airbag device is provided at the center of a steering wheel to protect an occupant from crashes occurring in a front-rear direction. Moreover, a curtain airbag device is often provided near the roof rail above a side window to protect occupants from an impact applied from a vehicle width (side impact) direction resulting from side crashes or the like, and a side airbag device may also be provided in a side portion of a seat.
The cushions of various airbag devices often have a structure designed by taking a desired behavior during deployment, occupant restraining force, and the like into consideration. For example, International Patent Publication No. WO2002/100691 discloses a side airbag device having a dual structure in which an inner bag is provided inside an outer bag. International Patent Publication No. WO2002/100691 discloses a configuration in which an inner bag is provided in a lower portion and the lower portion is inflated earlier than an upper portion to restrain the waist of an occupant with the high internal pressure.
The ribs of the chest of a person are narrower than the pelvis in the waist, and many vital internal organs are present in the chest. In general, when an occupant is restrained by the cushion of a side airbag device, the chest tends to have a higher injury level than the waist. Thus, the cushion of the side airbag device needs to suppress the load on the chest of an occupant.
In the side airbag device of International Patent Publication No. WO2002/100691, a vent hole is formed in an upper portion. The vent hole is a structure for discharging gas outside the airbag, and International Patent Publication No. WO2002/100691 describes that the stiffness of an airbag (cushion) is adjusted by the discharge of gas. However, when the position of the vent hole is taken into consideration as well as forming the vent hole, it is advantageous in realizing efficient gas discharge and adjusting the internal pressure of the cushion. Moreover, for example, although a method of increasing the diameter of the vent hole to increase a discharge amount can be considered, the energy absorption amount of the cushion may decrease if the diameter of the vent hole is increased too much.